1. Field of the Invention
The invention relates to a device for the voltage supply in a motor vehicle and, more particularly, to a device for supplying voltage in a motor vehicle having two batteries.
2. Prior Art
Until now, the voltage supply in motor vehicles was typically done with the aid of a single battery charged by a generator. In modern motor vehicles with many electrical consumers, one battery is sometimes no longer sufficient for the voltage supply, and so two separate batteries are used that typically connected parallel to one another. To assure that the two batteries will not deleteriously affect one another, and thus to keep voltage drops that can occur during actuation of the starter away from voltage-critical components, a charging/disconnection module is connected between the two batteries, in a device for the voltage supply in a motor vehicle known from German Patent 41 38 943. During the starting process this module disconnects the battery connected with the starter from the rest of the on-board electrical system. Since the rated voltage of the battery connected to the starter is somewhat lower than the rated voltage of the on-board electrical system battery, it is assured that the starter battery will be optimally charged at all times. In one embodiment of the known device for the voltage supply in a motor vehicle, a voltage converter be used, for example a stepup device. It is thus possible to use a starter battery whose rated voltage is higher than that of the on-board electrical system battery. The charging voltage required for charging the starter battery can be obtained by increasing the voltage obtained from the on-board voltage.